fix u-boot build break with current master
fix u-boot build break with current master

The current yocto master adds a patch for the beaglebone to the u-boot.inc, which breaks the build.
Explicitly set SRC_URI to prevent that.

Signed-off-by: c7cadc32e09df788b3f17e67e85fdda426a6015f@jenslucius.com

linux-sunxi/meta-sunxi,geomatsi/meta-sunxi,linux-sunxi/meta-sunxi,ebutera/meta-sunxi,twoerner/meta-sunxi,soderstrom-rikard/meta-sunxi,linux-sunxi/meta-sunxi,geomatsi/meta-sunxi,jlucius/meta-sunxi,jlucius/meta-sunxi,jlucius/meta-sunxi,net147/meta-sunxi,net147/meta-sunxi,soderstrom-rikard/meta-sunxi,twoerner/meta-sunxi,ebutera/meta-sunxi